This invention relates to the manufacture of generator electromagnetic rotors, primarily for use in power generating equipment.
In conventional processes for manufacturing generator electromagnetic rotors, the current-carrying copper coils (called xe2x80x9cfield coilsxe2x80x9d) are laboriously hand insulated. Each coil must be insulated from other coils, and the entire coil package must be insulated from the steel of the rotor. Significant cost savings and productivity improvements could be realized with a simpler and faster insulation system.
It is now proposed to coat the copper field coils with a suitable powder resin. The coating can be applied by electrostatic spraying or other suitable process. In one technique, the field coils remain stationary while electrostatic spray guns revolve around the coils. In an alternative technique, the coils are carried along a conveyor through a power spray booth. With either technique, the resin powder can be cured onto the field coils using resistance heating, induction heating, convection heating or infrared heating. Two coats of the resin powder are required to ensure complete coverage. In addition, and depending on the coil configuration, the ends of the copper bars may be masked to prevent powder coverage where not desired (for example, at the site of the electrical connections).
Three classes of powder resins have the greatest potential for success in this particular application. They are epoxy powder coating resins, silicone powder coatings and hybrid systems of silicones/epoxies and silicones/acrylics. These materials have been shown to have high dielectric strength, impact strength, thermal stability, flexibility, chemical resistance and adhesion.
Thus, in accordance with its broader aspects, the present invention relates to a field coil for an electromagnetic rotor comprising multiple windings, each substantially entirely coated with a powder resin having a dielectric strength of at least in the range of 1000-1500 v/mil.
In another aspect, the winding relates to a field coil for an electromagnetic rotor comprising a field coil substantially entirely coated with a powder resin selected from a group consisting essentially of epoxy powder resins and silicone powder resins.
In another aspect, the invention provides a method of insulating a field coil for an electromagnetic generator comprising:
a. providing field coils comprising multiple layers of copper bars;
b. coating the multiple layers of the field coil with a powder resin having a dielectric strength of at least about 1000-1500 v/mil.; and
c. curing the powder resin.